1. Field of the Invention
The present invention relates to a light source device, an image reading apparatus, and an image reading method. In particular, it relates to a light source device which is capable of suppressing change of state of emitted light, resulting from variation of temperature, and an image reading apparatus equipped with the light source device, and also to an image reading method in the image reading apparatus.
2. Description of the Related Art
In recent years, image reading apparatuses have been put to practical use, wherein illuminating light is applied to a reflection original such as a photographic print, or a transmission original such as a photographic film, and reflected light or transmitted light from the original which carries image information to be recorded thereon, is received by an image sensor such as a charge coupled device (CCD) so as to allow reading of an image recorded on the original, and various corrections are made for image data obtained by the reading, and thereafter, the image is recorded on a recording material such as photographic printing paper, or the image is shown on a display. Such image reading apparatuses have an advantage in that automation of an operation from reading of an image recorded on an original to recording of the image on a recording material or displaying of the image on a display is facilitated.
In this kind of image reading apparatus, a white light source such as a halogen lamp has been conventionally employed as a light source which applies light to an original. Recently, an apparatus using an LED light source in place of the white light source has been put to practical use, which LED light source includes a large number of light emitting diodes (LED) which emit light of red (R), green (green), and blue (B) (additionally, infrared (IR) light may also be used to detect a defect position) are arranged on a substrate.
Due to the LED light source as described above being applied, no filter provided for color separation of the white light source is required, and the structure of the apparatus becomes simple. Further, setting of conditions of each color balance or the like can also be simplified.
However, in the LED light source used by the image reading apparatus described above, when an environmental temperature at the position where the LED light source is disposed, changes or when variation of temperature is caused by generation of heat from the light source itself, the wavelength of light emitted from the light source or the amount of emitted light changes. Therefore, there exists a problem in that image data read at the time before and after variation of temperature may change and image data of high quality cannot be obtained.
In order to solve the above-described problem, the technique disclosed in Japanese Patent Application Laid-Open (JP-A) No. 7-175035 can be applied, wherein a Peltier element (a Peltier device) is contact fixed to a reverse surface of a light source or a reflection plate, and a temperature sensor is provided in the vicinity of the light source, and temperature control is effected so that the temperature detected by the temperature sensor becomes a set value.
However, in the technique disclosed in JP-A No. 7-175035, a Peltier element having a great amount of radiation heat is used to adjust the temperature of the light source. Therefore, a large-size fan is required for discharging radiation heat. As a result, there exists a problem in that an entire apparatus is made larger.
Further, in the technique in which a Peltier element is used for temperature control, which includes the technique disclosed in JP-A No. 7-175035, generally, when the Peltier element is mounted at a position at which the temperature is adjusted, it is adhesion fixed to the position by using an adhesive having a high thermal conductivity. Therefore, there exists a problem in that assembling efficiency and maintenability are poor.
Moreover, the technique disclosed in JP-A No. 7-175035 has a problem in that, when the temperature of the light source is rapidly raised by the Peltier element, moisture condensation may be caused in the light source or members provided in the vicinity of the light source. In this case, there exist problems in that the apparatus is apt to fail, and when moisture condensation occurs in the light source, uniformity of light emitted from the light source is not maintained, thereby resulting in no high quality image data being obtained.